The present invention relates to a novel fluorine-containing polymer having an acid-reactive group, and further relates to a material for a fluorine-containing base polymer which has a high transparency against energy rays (radioactive rays) in a vacuum ultraviolet region and is suitable for use on a photoresist and relates to a chemically amplifying type photoresist composition prepared therefrom.
As a result of an increasing necessity for high integration of a large scale integrated circuit (LSI), microfabrication technology is required for photolithography technology. In order to satisfy such requirements, there have been attempts to use, as exposure light sources, a deep ultraviolet, a KrF excimer laser (wavelength: 248 nm) and a ArF excimer laser (wavelength: 193 nm) which have a wavelength shorter than conventional g-rays (wavelength: 436 nm) and i-rays (wavelength: 365 nm). Those light sources are put into practical use.
Recently a process using a F2 laser (wavelength: 157 nm) having a wavelength in a vacuum ultraviolet region has been studied in a ultra-microfabrication technology and is considered promising as an exposure technology aiming at a technology node of 0.1 μm.
On the other hand in the pattern formation, a chemically amplifying type resist which becomes advantageous in transparency, resolution, sensitivity and dry etching resistance in cases of energy rays having various wavelengths has been studied. The chemically amplifying type resist means, for example, in case of a positive resist, an energy-sensitive composition comprising a resin soluble in an alkali developing solution and having an introduced substituent which has an effect of inhibiting dissolution of the resin but is deprotected due to action of an acid, and a compound which generates an acid by irradiation of energy rays such as light and electron beam (hereinafter referred to as a photoacid generator). When the composition is irradiated with light or electron beam, an acid is generated from the photoacid generator, and by heating (post-exposure bake, hereinafter referred to as “PEB”) after the exposure of light, the substituent which has been giving a dissolution inhibiting effect on the resin is deprotected due to action of an acid. As a result, the exposed portion becomes soluble in alkali, and by treating the exposed portion with an alkali developing solution, a positive resist pattern can be obtained. In that case, the acid acts as a catalyst and exhibits its effect in a very small amount. Also action of the acid becomes active by the PEB and a chemical reaction is accelerated like a chain reaction, and thus sensitivity is enhanced.
Examples of conventional resins used for such a chemically amplifying type resist are phenol resins, a part or a whole of hydroxyl groups of which is protected by protective groups such as acetal and ketal (KrF resist), methacrylic acid resins in which an acid-labile ester group acid is introduced into carboxyl group (ArF resist) and the like.
However there is a basic problem that those conventional polymers for a resist have a strong absorption in a wavelength range of a vacuum ultraviolet region and transparency thereof is low (molecular absorption coefficient is large) in a F2 laser having a wavelength of 157 nm which have been studied for use in a ultra-microfabrication process. Therefore in case of exposure with a F2 laser, it is necessary to make a thickness of the resist extremely thin, and substantially it is difficult to use those polymers as a single layer F2 resist.
R. R. Kunz, T. M. Bloomstein, et al. made a comparison of transparency of various materials at a wavelength of 157 nm and disclosed in Journal of Photopolymer Science and Technology (Vol. 12, No.4 (1999), pp 561-569) that fluorocarbons have good transparency, which suggests possibility of use thereof as the F2 resist.
However that publication only describes that the existing fluorocarbon polymers have a high transparency at a wavelength of 157 nm but does not describe a concrete preferred structure of a fluorine-containing polymer. Also, for example, with respect to a fluorine-containing polymer having a functional group necessary for a chemically amplifying type positive or negative resist, neither evaluation of its transparency nor its synthesis was made. Further there was no suggestion at all with respect to a fluorine-containing base polymer material preferable for a chemically amplifying type resist and a preferable resist composition prepared from such a material, and there was found no possibility of forming a F2 resist pattern by using a fluorine-containing polymer.
Thereafter A. E. Feiring, et al. of E.I. du Pont de Nemours and Company disclosed in PCT patent publication No. WO00/17712 (laid open on Mar. 30, 2000) that a specific fluorine-containing polymer is useful for F2 resist application.
That PCT patent publication discloses use of a fluorine-containing polymer comprising a structural unit of fluoroolefin and a structural unit having a polycyclic structure, but a fluorine-containing polymer not having a polycyclic structure, for example, a fluorine-containing ethylenic polymer having a chain structure is not disclosed therein.
Also, introduction of an acid-labile (or an acid-degradable) functional group which is necessary for a positive resist, into a fluorine-containing polymer has been carried out by copolymerizing a monomer obtained by introducing an acid-labile (or an acid-degradable) functional group into a conventional acrylic, methacrylic, norbornene or vinyl ester monomer. However there is no disclosure with respect to use of a monomer having both of fluorine atom or fluoroalkyl group and an acid-labile (or an acid-degradable) functional group.
Also, there is disclosed a norbornene derivative and halogen-substituted norbornene as an example of a polycyclic structure constituting a fluorine-containing polymer for use in a resist. However concretely there is no disclosure as to fluorine substitution, simultaneous substitution of fluorine atom and an acid-reactive group in one molecule and further substitution at a specific position.
Further thereafter A. E. Feiring, et al. of E.I. du Pont de Nemours and Company disclosed in PCT patent publication No. WO00/67072 (laid open on Nov. 9, 2000) that a fluorine-containing polymer having —C(Rf)(Rf′)OH or —C(Rf)(Rf′)O—Rb is useful for F2 resist application.
The above-mentioned PCT patent publication discloses an introduction of —C(Rf)(Rf′)OH or —C(Rf)(Rf′)O—Rb into a fluorine-containing polymer by copolymerization of a norbornene derivative or an ethylenic monomer having —C(Rf)(Rf′)OH or —C(Rf)(Rf′)O—Rb but discloses no fluorine-containing polymer having a structural unit of a fluorine-containing monomer having a functional group which is converted to carboxyl group by a reaction with an acid.
Also, norbornene derivatives having —C(Rf)(Rf′)OH or —C(Rf)(Rf′)O—Rb are disclosed as one example of fluorine-containing polymers for use in a resist, and a halogen-substituted norbornene is also described therein. However concretely there is no disclosure as to fluorine substitution, simultaneous substitution of fluorine atom and an acid-reactive group (particularly a functional group to be converted to carboxyl group by a reaction with an acid) in one molecule and further substitution at a specific position.
The first object of the present invention is to provide a novel fluorine-containing polymer having an acid-reactive group and usable as a polymer for a resist and to provide a coating film thereof.
The second object is to provide a fluorine-containing base polymer material which has a high transparency at a wavelength in a vacuum ultraviolet region (for example, 157 nm), is usable as a base polymer for a chemically amplifying type photoresist, and has an introduced acid-reactive group.
Further the third object is to provide a chemically amplifying type photoresist composition which comprises a fluorine-containing polymer having an acid-reactive group and a photoacid generator and is usable for a patterning process using a F2 laser as a light source, and to provide a coating film obtained by coating the composition.
Further Katsuyama, et al. of Matsushita Electric Industrial Co., Ltd. have proposed a method of forming a pattern by exposure of light having a wavelength within the range of from 1 to 180 nm by using a resist material having halogen atom, etc. (JP-A-2000-321774, laid open on Nov. 24, 2000). However only a methacrylic resin having a structural unit of methacrylic acid ester having —CH2CF3 group or —CH(CF3)2 group on its side chain is disclosed as a base resin having halogen atom for a resist, and there is disclosed neither a resin having fluorine atom on its trunk chain nor a polymer which has a structural unit of fluorine-containing monomer having fluorine atom and a functional group simultaneously and can be used for a chemically amplifying type resist (positive or negative). Further there is no disclosure as to a polymer having a ring structure on its trunk chain.